Stability controls in subsurface interfaces subjected to thermal and mechanical actions


   School of Energy, Geoscience, Infrastructure and Society

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  Dr M Sutman  No more applications being accepted  Competition Funded PhD Project (Students Worldwide)

About the Project

Fully funded PhD position available to UK and international students! Apply by 12 noon, 5 January 2024 (international applicants must have contacted supervisor by 11 December 2023).

Understanding the response of geo-materials and civil infrastructure to thermo-mechanical actions is crucial for the shallow geothermal energy exploitation. Energy geostructures enable the use of renewable energy sources for efficient heating and cooling of buildings, by combining their conventional structural support role with the contemporary one of heat exchange [1, 2]. Therefore, any structure (energy piles, walls, tunnels) in contact with geo-materials can be equipped with geothermal loops, connected to a ground source heat pump, allowing heat exchange with the ground (Fig. 1). Energy geostructures research has so far focused on in-situ tests [3], laboratory-scale tests [4] and numerical tools [5], aiming to understand cyclic temperature change effects (triggered by geothermal operations) on the behaviour of geomaterials, infrastructures and their interfaces. Yet, emphasis was on soils and soil-concrete interfaces, overlooking the impact of shallow rock formations. The latter has recently attracted concerns following an in-situ test on energy piles whose bottom portions were socketed in sandstone [6]. Results showed that the pile portion within the sandstone experienced tensile stresses during heat injection into the ground; the inverse of what would be expected had the pile been embedded entirely in soils. Although this observation was attributed to larger thermal expansion of sandstone (vs that of soil or concrete), a thorough understanding of this phenomenon has never been investigated to date.

The thermo-mechanical response of soil-rock interfaces can also be linked to the global temperature increase (up to 10˚C in cities by 2080), which will affect soils, rocks and their interface particularly in shallow depths. Finally, undisturbed ground temperature is highly affected by human activities, such as the operation of underground systems, which increases the ground temperature in urban environments (5-14˚C temperature increase around London Underground). Considering infrastructure in mixed-face ground, the soil-rock interaction will become increasingly crucial due to temperature variations.

Extensive research was performed on mechanical behaviour of soil-structure interfaces [7], limited efforts were also devoted to temperature effects on soil-concrete interfaces [8]. According to these studies, depending on the concrete surface roughness and soils’ mean grain size, three failure mechanisms can occur: shear failure within the soil for rough surface, sliding at the interface for smooth surface, simultaneous shear and sliding at roughness close to the critical one. Limited research on thermal effects showed that sand-concrete interface has fairly thermo-elastic behaviour whereas clay-concrete interface shows decrease in interface friction angle and increase in adhesion with temperature rise. Yet, how the aforementioned knowledge can be applied to soil-rock interfaces is still obscure due to several differences concrete and rock interfaces possess: (i) soils around concrete structures are usually disturbed due to construction efforts, the ones around rock formations are naturally deposited over long geological periods; (ii) concrete structures usually have uniform roughness, rock surfaces might have irregularities; (iii) concrete structures are usually accepted as isotropic, rock formations can exhibit highly anisotropic behaviour. Regarding these disparities, an extensive experimental investigation of soil-rock interfaces considering confining pressure, surface impurities and rock anisotropy is essential, the outcomes of which will benefit geoenergy, climate change and urban heat island fields.

Aims

The objective of this project is to forge an observational framework in understanding the fundamental mechanics of soils, rock formations and their interaction in consequence of thermo-mechanical actions through a cross-scale experimental campaign. The outcomes will help predict potential soil-rock interface deformation and failure triggered by thermal variations, potentially leading to engineering strengthening of the geomaterials in contact.

Objectives

The objectives are summarised below:

O1: Investigation of the soil-rock interfaces subjected to mechanical (M) and thermo-mechanical (TM) actions in macro-scale.

O2: Investigation of the soil-rock interfaces subjected to M and TM actions in meso-scale.

O3: Examination of geomaterial and environmental effects on the response of soil-rock interface in micro-scale.

O4: Assessment of key mechanisms leading the behaviour of soil-rock interfaces.

Further project details can be found on the IAPETUS website.

Eligibility

Eligibility is under UKRI Terms and Conditions, which means that UK and International candidates may apply. For International Students, UKRI only pay the equivalent of home fees. The differential between home and international fees will likely need to be self-funded. International applicants need to contact the primary supervisor of the project (Dr Melis Sutman [Email Address Removed]) by no later than Monday 11th December 2023 in order to be considered for shortlisting.

How to Apply

All prospective students need to complete the online IAPETUS2 form (link here). Before completing this form, please read the DTP privacy policy as you will need to tick that you have read and understood this.

Both parts of the application must be made by Friday 5th January 2023 at 12pm (GMT), which is the public deadline for applications that will apply across all of the Partnership. 

Engineering (12) Geology (18)

Funding Notes

IAPETUS2’s postgraduate scholarships are tenable for up to 3.5 years and provide the following package of financial support:
A tax-free maintenance grant set at the UK Research Council’s national rate, which in 2023/24 is £18,622;
Payment of tuition fees at the Home rate*;
Access to extensive research support funding; &
Support for an external placement of up to six months.
Part-time award-holders are funded for seven years and receive a maintenance grant at 50% of the full-time rate.
*Eligibility is under UKRI terms and conditions. International Students can apply but it is expected that the differential between home and international fees will likely be self-funded.

References

[1] Sutman, M., Speranza, G., Ferrari, A., Larrey-Lassalle, P., Laloui, L., 2020. Long-term performance and life cycle assessment of energy piles in three different climatic conditions. Renewable Energy, 146, pp.1177-1191.[2] Laloui, L. and Sutman, M., 2023. Energy geotechnology: A new era for geotechnical engineering practice. In Smart Geotechnics for Smart Societies (pp. 45-61). CRC Press.[3] Sutman, M., Brettmann, T., Olgun, C.G., 2019. Full-scale in-situ tests on energy piles: Head and base-restraining effects on the structural behaviour of three energy piles. Geomechanics for Energy and the Environment, 18,pp.56-68.[4] Hashemi, A., Sutman, M. and Medero, G.M., 2023. A review on the thermo-hydro-mechanical response of soil–structure interface for energy geostructures applications. Geomechanics for Energy and the Environment, p.100439.[5] Sutman, M., Olgun, C.G., Laloui, L., 2018. Cyclic Load–Transfer Approach for the Analysis of Energy Piles. Journal of Geotechnical and Geoenvironmental Engineering, 145(1), p.04018101.[6] RottaLoria, A.F., Laloui, L., 2016. Thermally induced group effects among energy piles. Géotechnique, 67(5), pp.374-393.[7] Dejong, J.T., White, D.J., Randolph, M.F., 2006. Microscale observation and modeling of soil-structure interface behavior using particle image velocimetry. Soils and foundations, 46(1), pp.15-28.[8] Di Donna, A., Ferrari, A., Laloui, L., 2015. Experimental investigations of the soil–concrete interface: physical mechanisms, cyclic mobilization, and behaviour at different temperatures. Canadian Geotechnical Journal, 53(4), pp.659-672.
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